High temperature-stabile silicon boron carbide nitride ceramics comprised of silylalkyl borazines,method for the production thereof, and their use

ABSTRACT

The present invention concerns a process for producing silylalkylboranes containing the structural feature Si—C—B, new molecular silylalkylboranes, new molecular silyalkylborazines, new oligoborocarbosilazanes and polyborocarbosilazanes, a process for their production and their use as well as silicon boron carbide nitride ceramics and a process for their production.

DESCRIPTION

[0001] The present invention concerns a process for producingsilylalkylboranes containing the structural feature Si—C—B, newmolecular silylalkylboranes, new molecular silylalkylborazines, newoligoborocarbosilazanes and polyborocarbosilazanes, a process for theirproduction and their use, as well as high-carbon silicon boron carbidenitride ceramics and a process for their production.

[0002] The production of non-oxidic multinary ceramics by cross-linkingmolecular precursors is of supreme importance. Ceramic materials of highpurity which have a homogeneous distribution of elements at the atomiclevel can at present only be produced by this method. Such materialscannot be prepared by means of conventional synthetic pathways such assolid-state reactions.

[0003] Nitride and carbide-nitride ceramics containing boron and siliconhave become particularly important. They have a high thermostability andoxidation resistance and exhibit a pronounced crystallizationinhibition. The thermal stability of ceramics in this quarternary systemcan be increased by additionally incorporating carbon into the ceramicnetwork. Such materials are excellently suitable for use at hightemperatures under atmospheric conditions and can be used as a bulkmaterial, as ceramic fibres in composite materials, the form of coatingsor they can be used for microstructural processes.

[0004] The synthesis of the single component precursortrichlorosilylaminodichloroborane (TADB, Cl₃Si—NH—BCl₂) is described inthe patent DE 4 107 108 A1 which results in a ceramic of the approximatecomposition SiBN₃ after cross-linking with methylamine and subsequentpyrolysis in a stream of inert gas. The carbon which it contains isderived from the methyl group of the cross-linking reagent methylamine.

[0005] A disadvantage of this process is the limited ability to vary thecarbon content which can only be adjusted by using a longer alkyl groupin the cross-linking reagent. However, this alkyl group is lost duringthe pyrolysis in the form of volatile hydrocarbons or it leads toundesired graphite deposits in the ceramic.

[0006] The patent WO 98/45302 describes the production of high-carbonceramics in the Si/B/N/C system from a single-component precursor whichhas a branched carbon bridge between the elements boron and silicon.This allows the synthesis of ceramics which have a higher carboncontent. A disadvantage of this process is that the single-componentprecursor has an alkyl group at the carbon bridge which can be lostduring pyrolysis in the form of volatile hydrocarbons.

[0007] Hence an object of the present invention was to provide a simpleprocess which yields the single-component precursor in high yields anddoes not have the disadvantages of the prior art. In particular theprocess should also allow the preparation of precursor compounds withoutbranched alkyl groups which can then be further processed to amorphousor partially crystalline high carbon ceramics.

[0008] Another object was to provide amorphous Si/B/N/C ceramics, havingan improved high temperature and oxidation stability.

[0009] This object is achieved according to the invention by a processfor producing a compound of formula (I)

(R)₃Si—C(R¹)(R²)—B(R)₂  (I)

[0010] in which R in each case independently denotes a hydrocarbon with1 to 20 C atoms, hydrogen, halogen, NR′R″ or OR′ where R′ and R″independently of one another, denote hydrogen or a hydrocarbon with 1 to20 C atoms and

[0011] R¹ and R² denote independently of one another a hydrocarbon with1 to 20 C atoms, hydrogen, halogen, NR′R″ or OR′ where R′ and R″independently of one another, denote hydrogen or a hydrocarbon with 1 to20 C atoms.

[0012] In the process according to the invention a silane of the generalformula (II)

(R)₃Si—C(R¹)(R²)—X  (II)

[0013] in which X denotes halogen, is reacted with a metal M e.g. analkali metal such as Na, K and in particular Li, an alkaline earth metalin particular Mg or a transition metal such as Cu, Zn, Cd, Hg. Thereaction takes place at temperatures in which essentially nopolymerization occurs and in particular below 50° C. and particularlypreferably between 0° C. and 15° C. in an aprotic organic solvent andyields a silane of the general formula (III)

(R)₃Si—C(R¹)(R²)-M(X)_(w)  (III)

[0014] in which w=0 if M is a monovalent metal and

[0015] w is an integer ≧1 corresponding to the valence state of M minus1 if M is a multivalent metal.

[0016] As used in this application the residues R, R¹, R², R′ and R″ caneach independently denote a hydrocarbon residue with 1 to 20 C atoms,preferably with 1 to 10 C atoms. A hydrocarbon residue is a residuewhich is composed of the elements carbon and hydrogen. According to theinvention the hydrocarbon residue can be branched or unbranched,saturated or unsaturated. The hydrocarbon residue can also containaromatic groups which can in turn be substituted with hydrocarbonresidues. Examples of preferred hydrocarbon residues are e.g. unbranchedsaturated hydrocarbon residues such as C₁ to C₂₀ alkyl, in particularmethyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl,n-nonyl and n-decyl. However, the residues R can also be branchedsaturated hydrocarbon residues, in particular branched C₁ to C₂₀ alkylssuch as i-propyl, i-butyl, t-butyl and other branched alkyl residues. Inanother preferred embodiment the residue R contains one or more olefinicunsaturated groups. Examples of such residues are vinyl, allyl, butenyl,pentenyl, hexenyl, heptenyl, octenyl, nonenyl, decenyl, butadienyl,pentadienyl, hexadienyl, heptadienyl, octadienyl, nonadienyl anddecadienyl. The residue R can also contain an alkine group i.e. a C≡Cbond. In a further preferred embodiment at least one residue R andpreferably all residues R contain an aromatic group in particular anaromatic residue with 5 or 6 C atoms such as a phenyl group or a phenylgroup substituted with a hydrocarbon such as methylphenyl,dimethylphenyl, trimethylphenyl, ethylphenyl or propylphenyl. Thearomatic residue including the substituents preferably contains 5 to 20and in particular up to 10 C atoms. In this case the hydrocarbonresidues R, R¹, R², R′, R″ can each differ from one another.

[0017] At least one residue R, R¹, R², R′ or/and R″ and in particularall residues R, R¹, R², R′ and/or R″ particularly preferably contain aC₁ to C₂₀ alkyl group in particular a C₁-C₆ alkyl group, a phenyl group,a vinyl group or an allyl group or a hydrocarbon residue with 1 to 3 Catoms in particular methyl, ethyl or propyl and most preferably methyl.

[0018] The residue Hal represents a halogen atom and in particulardenotes Cl, Br or I and it is preferred that at least one residuedenotes Hal and preferably all Hal residues denote Cl.

[0019] As described above the compound (III) can, on the one hand, beproduced directly from a compound of formula (II) and a metal when ametal of sufficient reactivity is used e.g. Li, Na, K, Mg, Cu, Zn, Cd,Hg. On the other hand, a compound (III) in which M is a metal that isnot sufficiently reactive for an efficient direct alkylation e.g. Sn canalso be produced in two steps. In the first step a compound (III)containing a directly reactive metal is produced which is thentransmetallated in a second step with the not directly reactive metal.The metal can for example be used in the form of metal chips orpreferably as a powder.

[0020] Subsequently the compound of the general formula (III) is reactedat temperatures below 50° C. and preferably at temperatures between −50°C. and 0° C. with a borane of the general formula

Y—B(R)₂

[0021] in which R is as defined above and Y represents halogen, NR′R″ orOR′ where R′ and R″ independently of one another denote hydrogen or ahydrocarbon with 1 to 20 C atoms.

[0022] It is also possible to firstly transfer the silylalkyl residue offormula (III) onto another metal and then to carry out the reaction withthe borane.

[0023] In a preferred embodiment of the process a chloromethyl silanecompound of formula

(R)₃Si—CH₂Cl

[0024] in which R independently of one another can have the meaningsstated for the general process, is metallated in a Grignard reactionwith magnesium powder and subsequently reacted with the halogen-borane.

[0025] The metallation of chloromethyl-alkylchlorosilanes of the generalformula (R_(n))(Cl_(3-n))Si(CH₂Cl) in which n=0; 1; 2; 3; R=C₁-C₆ alkyl,vinyl, phenyl, hydrogen, halogen, alkylamino groups N(R′) (R″), alkyloxygroups OR′ where R′, R″ can independently of one another be C₁-C₆ alky,vinyl, phenyl, hydrogen or halogen, can for example take place indiethyl ether or tetrahydrofuran.

[0026] The silane of the general formula (III) is preferably reactedwith at least one alkyloxychloroborane YB(R³)(R^(3′)) in which Y denotesCl and R³ and R^(3′) independently of one another denote a C₁-C₂₀ alkoxyor phenyloxy residue.

[0027] The halogen boranes YB(R³)(R^(3′)) used in the process accordingto the invention are particularly preferably alkoxychloroboranes inwhich Y=Cl, Br and R³, R^(3′) independently of one another denote C₁-C₆alkoxy or phenyloxy residues.

[0028] Hence another subject matter of the present invention is thereaction of a compound of the general formula (V)

(R)₃Si—C(R¹)(R²)—B(OR′)(OR″)  (V)

[0029] with an element halogenide or an organic acid halogenide.

[0030] This results in the formation of a compound of the generalformula (IV)

(R)₃Si—C(R¹)(R²)—BX₂  (IV)

[0031] In this formula R, R¹ and R² each independently of one anotherrepresent hydrogen, halogen, a hydrocarbon residue with 1 to 20 C atoms,a residue N(R′)(R″) or a residue OR′ in which R″ and R′ independently ofone another denote hydrogen or a hydrocarbon residue with 1 to 20 Catoms and X denotes halogen.

[0032] R¹ and R² each preferably denote, independently of one another,either hydrogen or halogen.

[0033] In a preferred embodiment of the process according to theinvention the intermediate products (R)₃Si—C(R¹)(R²)—B(OR′) (OR″) arereacted without prior separation from the reaction mixture with elementchlorides or organic acid halogenides and in particular with borontrihalogenides to form

(R)₃Si—C(R¹)(R²)BX₂  (IV)

[0034] which considerably reduces the work required for the preparation.

[0035] In a preferred embodiment the Grignard reaction is carried outusing the dilution principle at temperatures below 50° C. in an aproticorganic solvent which can for example be an acyclic or cyclic ether or aC₅-C₈ alkane.

[0036] In order to isolate the pure substances, the solvent is removedby distillation and the product is either fractionally distilled atreduced pressure or purified by recrystallization. Other purificationmethods can also be used such as e.g. high-performance liquidchromatography (HPLC).

[0037] The process according to the invention can also be used toprepare silylalkylboranes of formula (I) that cannot be produced by theprocess of WO98/45302.

[0038] Hence the invention also concerns silylalkylboranes of formula(I)

(R)₃Si—C(R¹)(R²)—B(R)₂  (I)

[0039] in which R each independently of one another denotes hydrogen,halogen, a hydrocarbon residue with 1 to 20 C atoms, N(R′)(R″) or OR′ inwhich R′ and R″ each independently represent hydrogen or a hydrocarbonresidue with 1 to 20 C atoms, and R¹ and R² each independently denotehydrogen, halogen, N(R′)(R″) or OR′, in which R′ and R″ eachindependently represent hydrogen or a hydrocarbon residue with 1 to 20 Catoms.

[0040] R is preferably in each case independently C₁-C₆ alkyl, vinyl,phenyl, hydrogen, halogen, organylamino groups N(R′)(R″), organyloxygroups OR′ where R′, R″ independently of one another denote C₁-C₆ alkyl,vinyl, phenyl or hydrogen and R¹, R² are, independently of one another,hydrogen or one of its isotopes or halogen.

[0041] The silylalkylborane of formula (I) is preferably one in which atleast one of the residues R represents methyl or/and Cl. It is alsopreferred that R¹ and R² are each hydrogen.

[0042] R is particularly preferably in each case independently Cl and/orCH₃ and R¹ and R²=H.

[0043] Particularly preferred embodiments of the inventivesilylalkylboranes of formula (I) are compounds in which a halogen andtwo hydrocarbon residues or two halogens and one hydrocarbon residue arebound to the Si. Such compounds contain one or two hydrocarbon residueson the Si atom which can be used to further increase the carbon contentof a ceramic produced from such compounds. In addition such compoundshave a reduced content of halogen atoms that react to form oligomers orpolymers. As a result it is possible to produce oligomers or polymershaving a reduced degree of cross-linking and in particular polymers thathave an essentially linear structure. Furthermore compounds of formula(I) are preferred in which two halogen atoms or one halogen atom and onehydrocarbon residue are bound to the boron atom.

[0044] Single component precursors of this type in which boron andsilicon are linked by a bridge C(R¹)(R²) can be used to produce polymersin which carbon is a fixed constituent of the polymer independent of thedegree of cross-linking. This facilitates the incorporation of carboninto the ceramic network and substantially reduces the cleavage ofvolatile carbon-containing compounds during the pyrolysis. The C contentin the ceramic can be varied within wide limits by the selection of asuitable cross-linking reagent and as a result the spectrum ofproperties of the ceramics can be specifically adapted to therequirements. Ceramics produced in this manner have excellent hightemperature and oxidation stabilities.

[0045] The silanes used as the starting products are commerciallyavailable like the boron trihalogenides. The borane that is used can beprepared according to J. Chem. Soc. (1957) 501-505, from commerciallyavailable boranes.

[0046] The invention also concerns silylalkylborazines of formula (X):

[0047] in which R¹ each independently of one another denotes hydrogen,halogen, a hydrocarbon residue with 1 to 20 C atoms, N(R′)(R″) or OR′,in which R′ and R″ each independently represent hydrogen or ahydrocarbon residue with 1 to 20 C atoms and R² and R³ eachindependently denote hydrogen, halogen, N(R′)(R″) or OR′ in which R′ andR″ each independently represent hydrogen or a hydrocarbon residue with 1to 20 C atoms and R⁴ each independently represents R¹, Sn(R*)₃ orSi(R*)₃ in which R* each independently denotes R² or a hydrocarbonresidue with 1 to 20 C atoms.

[0048] The preferred and particularly preferred residues in the saidsilylalkylborazines correspond to the residues stated as being preferredfor silylalkylboranes.

[0049] The silylalkylborazines according to the invention areparticularly suitable as precursor compounds and, after polymerizationand pyrolysis of the polymers, lead to new amorphous Si/B/N/C ceramicshaving improved high temperature and oxidation stabilities which werepreviously unattainable in this system. These new ceramics exhibitalmost no loss in mass up to at least 2000° C. or/and are oxidativelystable up to at least 1400° C. in pure oxygen.

[0050] The silylalkylboranes according to the invention can be reactedwith amines of the type N(R⁴)₃ or with the corresponding ammonium saltsHN(R⁴)₃ ⁺A⁻ to form the described silylalkylborazines, in which R⁴ ineach case independently has the above-mentioned meanings. A⁻ representsany anion and is in particular a halogenide such as F⁻, Cl⁻, Br⁻ or I⁻,a SO₄ ²⁻ group, an NO₃ ⁻ group or a nitrite, chlorate, perchlorate,carbamate, tartrate, phosphate, pentaborate, chromate, citrate,hydrogencitrate, carbonate, hydrogencarbonate, triflate, acetate orbenzoate group. A⁻ is preferably a halogenide and particularlypreferably a chloride.

[0051] The reaction of the silylalkyiboranes with the amines or ammoniumsalts preferably takes place with or without solvent at temperaturesbetween −100° C. and 200° C., more preferably at temperatures between20° C. and 50° C.

[0052] Another process for producing silylalkylborazines starts withborazines of the type

[0053] in which R⁴ in each case independently of one another representshydrogen, halogen, a hydrocarbon residue with 1 to 20 C atoms, N(R′)(R″)or OR′, in which R′ and R″ each independently represent hydrogen or ahydrocarbon residue with 1 to 20 C atoms, Sn(R*)₃ or Si(R*)₃ in which R*each independently has the same meanings as R.

[0054] These borazines are reacted in the presence of a suitablecombination of catalyst, base and acid trap (e.g. a zeolite) withsilanes of the aforementioned formula (III) or with silanes of the type

[0055] wherein each R¹ independently denotes hydrogen, halogen, ahydrocarbon residue with 1 to 20 C atoms, N(R′)(R″) or OR′, in which R′and R″ each independently represent hydrogen or a hydrocarbon residuewith 1 to 20 C atoms, and R² and R³ each independently denote hydrogen,halogen, N(R′)(R″) or OR′ in which R′ and R″ each independentlyrepresent hydrogen or a hydrocarbon residue with 1 to 20 C atoms, Xdenotes hydrogen, halogen, Sn(R*)₃ or Si(R*)₃ in which each R*independently has the same meanings as R for the silylalkylborazines.

[0056] A borazine is particularly preferably used in this reaction inwhich the R⁴ on the boron represents halogen and R⁴ on the nitrogenrepresents hydrogen and a silane is used in which X=hydrogen.

[0057] The invention also concerns oligoborocarbosilazanes andpolyborocarbosilazanes which can be obtained from the molecularsilylalkylboranes or silylalkylborazines according to the invention,characterized in that each silicon atom has in a first coordinationsphere at least one carbon atom which is bound to a boron atoms and thisboron atom is additionally bound to two nitrogen atoms.

[0058] The oligoborocarbosilazanes or polyborocarbosilazanes inparticular have the structural units Si—C—B—N—B—C—Si, Si—C—B—N—Si—C—Bor/and B—C—Si—N—Si—C—B. The said structural features are, for betterclarity, linear sequences in which Si is of course always bound to fourneighbouring atoms, B and N are always bound to three neighbouring atomsand C is in each case bound to three or four neighbouring atoms. Thecorresponding bonding dashes have been omitted to improve the clarity,but can easily be read by a person skilled in the art. Branches canoccur at every atom.

[0059] The invention also concerns a process for producing such anoligoborocarbosilazane or polyborocarbosilazane in which asilylalkylborane of formula (I) or a silylalkylborazine of formula (X)is reacted at temperatures of −100° C. to 300° C. with a compoundR′R″NH, in which R′, R″ each independently represents hydrogen or ahydrocarbon residue with 1 to 20 C atoms.

[0060] The molecular silylalkylborane or silylalkylborazine according tothe invention is preferably reacted with at least the n-fold molaramount, in particular with at least the 2n-fold molar amount, where ndenotes the number of sites in the molecule that can be cross-linked,and more preferably with an excess of ammonia and/or an organylamine offormula H₂NR or HNR₂ in whicn R═H, C₁-C₆ alkyl, vinyl or phenyl per molesilylalkylborane with or without solvent at temperatures between −100°C. and 300° C.

[0061] The oligoborocarbosilazanes or polyborocarbosilazanes can also beformed from the precursor compounds, in particular the above-mentionedsilylalkylboranes or silylalkylborazines, by direct polymerization ofthe single component precursor, in particular by polycondensation attemperatures between −100° C. and 500° C. It is not necessary to useammonia or/and amines for the direct polymerization.

[0062] The invention also concerns a process which can be used to adjustthe rheological properties of the oligoborocarbosilazanes orpolyborocarbosilazanes which are produced in the form of liquid, viscousor solid polymers some of which are soluble and meltable by usingammonia or by temperature treatment. The degree of cross-linking of theoligoborocarbosilazanes or polyborocarbosilazanes can be adjusted by thetype of polymer formation. The use of ammonia or amines results inhighly cross-linked structures whereas mainly linear structures areobtained in the direct polymerization by temperature treatment e.g. at≦500° C., preferably at ≦300° C. Hence oligoborocarbosilazanes orpolyborocarbosilazanes having different desired rheological propertiescan be specifically prepared or the rheological properties ofoligoborocarbosilazanes or polyborocarbosilazanes can be modified by anappropriate aftertreatment.

[0063] The oligoborocarbosilazanes or polyborocarbosilazanes areproduced in the form of liquid, viscous or solid polymers some of whichare soluble and meltable and can be subjected to various mouldingprocesses, e.g. casting, spinning into fibres, pulling foils, preparingcoatings by various coating processes such as dip coating or spincoating, before they are for example converted into silicon boroncarbide nitride ceramics.

[0064] The invention additionally concerns a process for producing asilicon boron carbide nitride ceramic in which an oligoborocarbosilazaneor poyborocarbosilazane according to the invention having the structuralelement Si—C—B(N)—N or a silylalkylborane of formula (I) or asilylalkylborazine of formula (X) is pyrolyzed in an inert orammonia-containing atmosphere at temperatures between −200° C. and+2000° C. and subsequently calcined in an inert or ammonia-containingatmosphere at temperatures between 800° C. and 2000° C.

[0065] The inert atmosphere can be selected from a noble gas atmospherefor example an argon or helium atmosphere, a nitrogen atmosphere or anatmosphere of another inert gas which does not react with the reactionpartners under the reaction conditions between 800° C. and 1700° C.

[0066] In a preferred embodiment of the process according to theinvention the oligoborocarbosilazanes or polyborocarbosilazanes areheated for several hours at temperatures between 30 and 1000° C. Theyare subsequently preferably calcined in a nitrogen or argon atmosphereat temperatures between 1200 and 1600° C. and preferred heating rates of1-100 K/min to remove hydrogen.

[0067] The invention also concerns silicon boron carbide nitrideceramics produced by the process described above from theoligoborocarbosilazanes or polyborocarbosilazanes according to theinvention.

[0068] These ceramics preferably contain the N—Si—C—B—N structuralelement and in particular the structural unit Si—C—B—N—B—C—Si,Si—C—B—N—Si—C—B or/and B—C—Si—N—Si—C—B.

[0069] The ceramics according to the invention can be produced in thepyrolysis in a crystalline as well as in amorphous form. They arepreferably in the form of a silicon boron carbide nitride powder. Due totheir particularly advantageous properties, ceramics are preferred inwhich the elements N, Si, C and B are present in an amount of more than93% by weight, in particular of more than 97% by weight. The ceramicaccording to the invention has in particular a low oxygen content of <7%by weight, preferably <3% by weight and particularly preferably <1% byweight or <0.5% by weight.

[0070] The amorphous material can be crystallized to form a compositeceramic with at least one of the materials SiC, Si₃N₄, BN, C and B₄C byage-hardening at a temperature of more than 1400° C. In such a compositeceramic the components are essentially homogeneously dispersed on ananometre scale i.e. they are monodisperse. The composite ceramicsaccording to the invention are especially characterized by their hightemperature resistance and can be present completely or partially in acrystalline form in particular as a powder.

[0071] The oligoborocarbosilazanes or polyborocarbosilazanes, ceramicsand composite ceramics can be used to produce ceramic powders, ceramiccoatings, ceramic mouldings, ceramic foils, ceramic fibres or ceramicmicrostructures.

[0072] The silylalkylboranes, oligoborocarbosilazanes andpolyborocarbosilazanes according to the invention can be used in achemical vapour-phase deposition (CVD) or physical vapour-phasedeposition (PVD). Ceramic coatings can be prepared by coating substratesby means of CVD or PVD. The vapour-phase deposition can be carried outas described in the prior art (see e.g. DE 196 358 48).

[0073] Microstructures can for example be produced by injection mouldingor lithographic processes. The ceramics are suitable for manufacturingcomposite materials. The ceramics are particularly preferably producedin the form of fibres from which fabrics or meshes can for example bemanufactured which can be used to increase the strength or toughness ofother ceramics.

[0074] Another subject matter of the present invention is a process forproducing a compound of formula (I)

(R)₃Si—C(R¹)(R²)—B(R)₂  (I)

[0075] in which R in each case independently represents a hydrocarbonwith 1 to 20 C atoms, hydrogen, halogen, N(R′)(R″) or O(R′) where R′ andR″ independently of one another denote hydrogen or a hydrocarbon with 1to 20 C atoms and R¹ and R² independently denote hydrogen, halogen or ahydrocarbon with 1 to 20 C atoms. In the process according to theinvention a silane of the general formula (VI)

(R)₃Si—C(R¹)(R²)—X  (VI)

[0076] in which X denotes hydrogen, halogen or silyl residues is reactedwith a borane of the general formula (VII)

B(R)₃  (VII)

[0077] in the presence of a suitable combination of catalyst, base andacid trap in which R in each case independently represents a hydrocarbonwith 1 to 20 C atoms, hydrogen, halogen, N(R′)(R″) or O(R′) where R′ andR″ independently of one another represent hydrogen or a hydrocarbon with1 to 20 C atoms.

[0078] Yet another subject matter of the present invention is a processfor producing a compound of formula (I)

(R)₃Si—C(R¹)(R²)—B(R₂)  (I)

[0079] in which R in each case independently represents a hydrocarbonwith 1 to 20 C atoms, hydrogen, halogen, N(R′)(R″) or O(R′) where R′ andR″ independently of one another denote hydrogen or a hydrocarbon with 1to 20 C atoms and R¹ and R² independently denote hydrogen, halogen or ahydrocarbon with 1 to 20 C atoms, characterized in that a CH-acidiccompound of the general formula (VIII)

(R)₃Si—C(R¹)(R²)—H  (VIII)

[0080] is reacted in the presence of a suitable combination of catalyst,base and acid trap with a borane of the general formula (IX)

X—B(R)₂  (IX)

[0081] in which R is defined as above and X represents halogen, NR′R″ orOR′ where R′ and R″ independently of one another denote hydrogen or ahydrocarbon with 1 to 20 C atoms.

[0082] An inorganic ion exchanger or a zeolite can be used in the twoaforementioned processes as an acid trap.

[0083] The invention is elucidated in the following on the basis of someexamples:

EXAMPLES OF APPLICATION Example 1

[0084] Preparation of (trichlorosilyl) (dichloroboryl)methane

[0085] Reaction equations:

Cl₃Si—CH₂—Cl+Mg→Cl₃Si—CH₂—MgCl  (1)

Cl₃Si—CH₂—MgCl+Cl—B(OC₂H₅)₂→Cl₃Si—CH₂—B(OC₂H₅)₂+MgCl₂  (2)

Cl₃Si—CH₂—B(OC₂H₅)₂+2BCl₃→Cl₃Si—CH₂—BCl₂+2Cl₂B(OC₂H₅)3Cl₂B(OC₂H₅)→3C₂H₅Cl+BCl₃+B₂O₃[cat:AlCl₃]  (3)

[0086] chloromethyltrichlorosilane 201 mmol, 36.9 g magnesium 288 mmol,7.0 g bis(ethoxy)chloroborane 224 mmol, 23.3 g boron trichloride 488mmol, 57.2 g aluminium trichloride  19 mmol, 0.5 g

[0087] 7.0 g magnesium powder is suspended in 150 ml absolute diethylether. The reaction is started by adding a few drops ofchloromethyltrichlorosilane and optionally heating slightly. A solutionof 36.9 g chloromethyltrichlorosilane in 200 ml diethyl ether is addeddropwise to this suspension at 15° C. After the addition is completed,the reaction mixture is cooled to −78° C. and 23.3 gbis(ethoxy)chloroborane is added in one pour. The reaction mixture isheated to room temperature, the resulting magnesium chloride is removedby filtration and the filtrate is freed from solvent. 57.2 g borontrichloride is condensed on the residue at −78° C. The mixture is heatedto room temperature to remove excess boron trichloride and theby-product ethoxy-dichloroborane is catalytically decomposed with 0.5 galuminium trichloride. All volatile products are collected in a coldtrap and fractionally distilled.

[0088]¹H-NMR (300 MHz, C₆D₆): δ=1.62-¹¹B-NMR (96 MHz, C₆D₆):δ=58.61-¹³C-NMR (75 MHz, C₆D₆): δ=30.53 (d)-²⁹Si-NMR (60 MHz, C₆D₆):δ=3.13.

Example 2

[0089] Preparation of (dichloromethylsilyl) (dichloroboryl)methane

[0090] Reaction equations:

Cl₂(CH₃)Si—CH₂—Cl+Mg→Cl₂(CH₃)Si—CH₂—MgCl  (1)

Cl₂(CH₃)Si—CH₂—MgCl+Cl—B(OC₂H₅)₂→Cl₂(CH₃)Si—CH₂—B(OC₂H₅)₂+MgCl₂  (2)

Cl₂(CH₃)Si—CH₂—B(OC₂H₅)₂+2BCl₃→Cl₂(CH₃)Si—CH₂—BCl₂+2Cl₂B(OC₂H₅)3Cl₂B(OC₂H₅)→3C₂H₅Cl+BCl₃+B₂O₃[cat:AlCl₃]  (3)

[0091] chloromethylmethyldichlorosilane 197 mmol, 32.3g magnesium 288mmol, 7.0 g bis(ethoxy)chloroborane 224 mmol, 23.3 g boron trichloride488 mmol, 57.2 g aluminium trichloride  19 mmol, 0.5 g

[0092] 7.0 g magnesium powder is suspended in 150 ml absolute diethylether. The reaction is started by adding a few drops ofchloromethylmethyldichlorosilane and optionally heating slightly. Asolution of 32.3 g chloromethylmethyldichlorosilane in 200 ml diethylether is added dropwise to this suspension at 15° C. After the additionis completed, the reaction mixture is cooled to −78° C. and 23.3 gbis(etlloxy)chloro-borane is added in one pour. The reaction mixture isheated to room temperature, the resulting magnesium chloride is removedby filtration and the filtrate is freed from solvent. 57.2 g borontrichloride is condensed on the residue at −78° C. The mixture is heatedto room temperature to remove excess boron trichloride and theby-product ethoxydichloroborane is catalytically decomposed with 0.5 galuminium trichloride. All volatile products are collected in a coldtrap and fractionally distilled.

[0093]¹H-NMR (300 MHz, C₆D₆): δ=1.47 (CH₂); 0.47 (CH₃)-¹¹B-NMR (96 MHz,C₆D₆): δ=58.61-¹³C-NMR (75 MHz, C₆D₆): δ=29.28 (d)-²⁹Si-NMR (60 MHz,C₆D₆): δ=23.85.

Example 3

[0094] Preparation ofTris(dimethylamino)silyl-bis(dimethylamino)boryl-methane

[0095] Reaction equation:

Cl₃Si—CH₂—BCl₂+10(CH₃)₂NH→[(CH₃)₂N]₃Si—CH₂—B[N(CH₃)₂]₂+5(CH₃)₂NH₂Cl

[0096] (trichlorosilyl)(dichloroboryl)methane  75 mmol, 17.3 gdimethylamine 3810 mmol, 171.8 g

[0097] A solution of 17.3 g (trichlorosilyl) (dichloroboryl)methane in200 ml absolute hexane is added dropwise to a solution of 171.8 gdimethylamine in 200 ml absolute hexane. After heating the reactionmixture to room temperature, the resulting dimethylamine hydrochlorideis removed by filtration. The filtrate is freed from solvent and theresidue is fractionally distilled.

[0098]¹H-NMR (300 MHz, C₆D₆): δ=2.45 (SiNCH₃); 2.50 (BNCH₃).

Example 4

[0099] Reaction of (trichlorosilyl)(dichloroboryl)methane withmonomethylamine (trichlorosilyl)(dichloroboryl)methane  37 mmol, 8.5 gdimethylamine 1722 mmol, 53.5 g

[0100] A solution of 8.5 g (trichlorosilyl) (dichloroboryl)methane in120 ml absolute hexane is added dropwise to a solution of 53.5 gdimethylamine in 120 ml absolute hexane. After heating the reactionmixture to room temperature, the resulting monomethylamine hydrochlorideis removed by filtration and the filtrate is freed from solvent. Thepolyborocarbosilazane remains as a clear viscous residue.

Example 5

[0101] Reaction oftris(dimethylamino)silylbis(dimethylamino)borylmethane with ammonia(trichlorosilyl)(dichloroboryl)methane  32 mmol, 8.7 g ammonia 5000mmol, 85.0 g

[0102] 8.7 g tris(dimethylamino)silyl/bis(dimethylamino)boryl/methane isstirred into 85.0 g ammonia for 48 hours at −50° C. After removing theammonia by distillation, the polyborocarbosilazane remains as a whitesolid residue.

Example 6

[0103] Preparation of B,B′, B″-(trichlorosilylmethiyl)borazine

[0104] Reaction equations:

3Cl₃Si—CH₂—BCl₂+3(CH₃)₃Si—NH—SiCl₃→[Cl₃Si—CH₂—BNH]₃+3SiCl₃+3(CH₃)₃SiCl

[0105] (trichlorosilyl)(dichloroboryl)methane 36 mmol, 8.4 g(trichlorosilyl)(trimethylsilyl)amine 50 mmol, 11.2 g

[0106] A solution of 8.4 g (trichlorosilyl)(dichloroboryl)methane in 20ml hexane is added dropwise to a solution of 11.2 g(trichlorosilyl)(trimethylsilyl)amine in 50 ml hexane while stirring atroom temperature. After a reaction period of 18 h, all volatilecomponents are removed by distillation at 10 mbar and the residue isrecrystallized from dichloromethane.

[0107]¹H-NMR (300 MHz, C₆D₆): δ=0.61 (CH₂); 4.50 (NH)-¹³C-NMR (75 MHz,C₆D₆): δ=16.98-¹¹B-NMR (96 MHz, C₆D₆): δ=32.74.

Example 7

[0108] Preparation of B,B′, B″-(trichlorosilylmethyl)borazine

[0109] Reaction equations:

3Cl₃Si—CH₂—BCl₂+3(CH₃)₃Si—NH—Si(CH₃)₃→[Cl₃Si—CH₂—BNH]₃+6(CH₃)₃SiCl

[0110] (trichlorosilyl)(dichloroboryl)methane 43 mmol, 9.9 ghexamethyldisilazane 45 mmol, 7.3 g

[0111] 7.3 g hexamethyldisilazane is added dropwise to 9.9 g(trichlorosilyl) (dichloroboryl)methane while stirring at roomtemperature. After a reaction period of 12 h, all volatile componentsare removed by distillation in a high vacuum and the residue isrecrystallized from dichloromethane.

Example 8

[0112] Preparation of B,B′, B″-(metbyldichlorosilylmethyl)borazine

[0113] Reaction equations:

3Cl₂(CH₃)Si—CH₂—BCl₂+3(CH₃)₃Si—NH—SiCl₃→[Cl₂(CH₃)Si—CH₂—BNH]₃+3SiCl₃+3(CH₃)₃SiCl

[0114] (methyldichlorosilyl)(dichloroboryl)methane 62 mmol, 13.0 g(trichlorosilyl)(trimethylsilyl)amine 69 mmol, 15.4 g

[0115] A solution of 13.0 g (methyldichlorosilyl)(dichloroboryl)methanein 30 ml hexane is added dropwise to a solution of 15.4 g(trichlorosilyl)(trimethylsilyl)amine in 70 ml hexane while stirring atroom temperature. After a reaction period of 18 h, all volatilecomponents are removed by distillation at 10 mbar and the residue isrecrystallized from dichloromethane.

[0116]¹H-NMR (300 MHz, C₆D₆): δ=0.48 (CH₃); 0.49 (CH₂); 4.53(NH)-¹³C-NMR (75 MHz, C₆D₆): δ=6.84 (CH₃); 14.68 (CH₂)-¹¹B-NMR (96 MHz,C₆D₆): δ=33.60.

Example 9

[0117] Preparation of B,B′, B″-(methyldichlorosilylmethyl)borazine

[0118] Reaction equations:

3Cl₂(CH₃)Si—CH₂—BCl₂+3(CH₃)₃Si—NH—Si(CH₃)₃→[Cl₂(CH₃)Si—CH₂—BNH]₃+6(CH₃)₃SiCl

[0119] (methyldichlorosilyl)(dichloroboryl)methane 55 mmol, 11 .5 ghexamethyldisilazane 61 mmol, 9.8 g

[0120] 9.8 g hexamethyldisilazane is added dropwise to 11.5 g(methyldichlorosilyl) (dichloroboryl)methane while stirring at roomtemperature. After a reaction period of 12 h, all volatile componentsare removed by distillation in a high vacuum and the residue isrecrystallized from dichloromethane.

Example 10

[0121] Reaction of B,B′, B″-(trichlorosilylmethyl)borazine withmonomethylamine B,B′, BΔ-(trichlorosilylmethyl)borazine  26 mmol, 12.0 gdimethylamine 1500 mmol, 46.6 g

[0122] A solution of 8.5 g (trichlorosilyl) (dichloroboryl)methane in120 ml absolute hexane is added dropwise to a solution of 53.5 gdimethylamine in 120 ml absolute hexane. After heating the reactionmixture to room temperature, the resulting monomethylamine hydrochlorideis removed by filtration and the filtrate is freed from solvent. Thepolyborocarbosilazane remains as a clear viscous residue.

Example 11

[0123] Reaction of B,B′, B″-(methyldichlorosilylmethyl)borazine withMonomethyl Amine B,B′,B″-(methyldichlorosilylmethyl)borazine  22 mmol,11.5 g dimethylamine 1500 mmol, 46.6 g

[0124] A solution of 8.5 g (trichlorosilyl) (dichloroboryl)methane in120 ml absolute hexane is added dropwise to a solution of 53.5 gdimethylamine in 120 ml absolute hexane. After heating the reactionmixture to room temperature, the resulting monomethylamine hydrochlorideis removed by filtration and the filtrate is freed from solvent. Thepolyborocarbosilazane remains as a clear viscous residue.

1. Process for producing a compound of formula (I)(R)₃Si—C(R¹)(R²)—B(R)₂ in which R in each case independently denotes ahydrocarbon with 1 to 20 C atoms, hydrogen, halogen, NR′R″ or OR′ whereR′ and R″ independently of one another, denote hydrogen or a hydrocarbonwith 1 to 20 C atoms and R¹ and R² independently of one another denotehydrogen, halogen, a hydrocarbon with 1 to 20 C atoms, NR′R″ or OR′where R′ and R″ independently of one another denote hydrogen or ahydrocarbon with 1 to 20 C atoms, characterized in that a silane of thegeneral formula (II) (R)₃Si—C(R¹)(R²)—X,  in which X denotes halogen isreacted with a metal M at temperatures below 50° C. in an aproticorganic solvent to form a silane of the general formula (III)(R)₃Si—C(R¹)(R²)-M(X)_(w)  in which w=0 if M is a monovalent metal and wis an integer ≧1 corresponding to the valence stage of M minus 1 if M isa multivalent metal, and the compound of the general formula (III) issubsequently reacted at temperatures below 50° C. with a borane of thegeneral formula Y—B(R)₂  in which R is defined as above and Y representshalogen, NR′R″ or OR′where R′ and R″ independently of one another denotehydrogen or a hydrocarbon with 1 to 20 C atoms.
 2. Process as claimed inclaim 1, characterized in that a chloromethyl-silane compound of formula(R)₃Si—CH₂Cl  in which R can in each case independently have themeanings stated in claim 1, is metallated with magnesium powder in aGrignard reaction and subsequently reacted with the halogenborane. 3.Process as claimed in one of the claims 1 or 2, characterized in thatthe silane of the general formula (III) is reacted with at least onealkyloxy-chloroborane XB(R³)(R^(3′)) in which X denotes Cl and R³ andR^(3′) independently of one another represent a C₁-C₂₀ alkoxy orphenyloxy residue.
 4. Process for producing a compound of the generalformula (IV) (R)₃Si—C(R¹)(R²)—B(X)₂,in which R, R¹ and R² in each caseindependently of one another denotes hydrogen, halogen, a hydrocarbonresidue with 1 to 20 C atoms, a residue N(R′)(R″) or a residue OR′ whereR″ and R′ independently of one another represent hydrogen or ahydrocarbon residue with 1 to 20 C atoms and X denotes halogen,characterized in that a compound of the general formula (V)(R)₃Si—C(R¹)(R²)—B(OR′)(OR″)  is reacted with an element halogenide oran organic acid halogenide.
 5. Process as claimed in claim 4,characterized in that R¹ and R² each independently of one another denotehydrogen or halogen.
 6. Molecular silylalkylborane of the generalformula (I) (R)₃Si—C(R¹)(R²)—B(R)₂ in which R each independently of oneanother denotes hydrogen, halogen, a hydrocarbon residue with 1 to 20 Catoms, N(R′)(R″) or OR′ in which R′ and R″ each independently representhydrogen or a hydrocarbon residue with 1 to 20 C atoms, and R¹ and R²each independently denote hydrogen, halogen, N(R′)(R″) or OR′, in whichR′ and R″ each independently represent hydrogen or a hydrocarbon residuewith 1 to 20 C atoms.
 7. Molecular silylalcylborane as claimed in claim6, characterized in that at least one of the residues R representsmethyl or/and Cl.
 8. Molecular silylalkylborane as claimed in claim 6 or7, characterized in that R¹ and R² are in each case hydrogen. 9.Silylalkylborazine of formula (X):

in which R¹ each independently denotes hydrogen, halogen, a hydrocarbonresidue with 1 to 20 C atoms, N(R′)(R″) or OR′, in which R′ and R″ eachindependently represent hydrogen or a hydrocarbon residue with 1 to 20 Catoms and R² and R³ each independently denote hydrogen, halogen,N(R′)(R″) or OR′ in which R′ and R″ each independently representhydrogen or a hydrocarbon residues with 1 to 20 C atoms and R⁴ denotesR¹, Sn(R*)₃ or Si(R*)₃ in which R* each independently denotes R² or ahydrocarbon residue with 1 to 20 C atoms
 10. Process for the productionof a silylalkylborazine as claimed in claim 9, characterized in that asilylalkylborane of formula (I) as defined in one of the claims 6 to 8is reacted with an amine N(R⁴)₃ or an ammonium salt HN(R⁴)₃ ⁺ in whichR⁴ has the meaning stated in claim 1 and A⁻ represents an anion. 11.Process for producing a silylalkylborazine as claimed in claim 9,characterized in that a borazine of formula (XI)

 in which R⁴ in each case independently of one another denotes hydrogen,halogen, a hydrocarbon residue with 1 to 20 C atoms, N(R′)(R″) or OR′,in which R′ and R″ each independently represent hydrogen or ahydrocarbon residue with 1 to 20 C atoms, Sn(R*)₃ or Si(R*)₃ in which R*each independently has the same meaning as stated for R in claim 1, isreacted with silanes of the type

 in which each R¹ independently of one another denotes hydrogen,halogen, a hydrocarbon residue with 1 to 20 C atoms, N(R′)(R″) or OR′,in which R′ and R″ each independently represent hydrogen or ahydrocarbon residue with 1 to 20 C atoms, and R² and R³ eachindependently denote hydrogen, halogen, N(R′)(R″) or OR′ in which R′ andR″ each independently represent hydrogen or a hydrocarbon residue with 1to 20 C atoms, X denotes hydrogen, halogen, Sn(R*)₃ or Si(R*)₃ in whichR* each independently has the same meanings as R. 12.Oligoborocarbosilazane or polyborocarbosilazane obtainable from acompound of formula (I) as claimed in one of the claims 6 to 8 or from acompound of formula (X) as claimed in claim 9, characterized in that ithas the structural feature


13. Process for the production of an oligoborocarbosilazane orpolyborocarbosilazane as claimed in claim 12, characterized in that asilylalkylborane obtainable by a process as claimed in one of the claims1 to 5 or a silylalkylborane as claimed in one of the claims 6 to 8 or asilylalkylborazine as claimed in claim 9 is reacted at temperatures of−100° C. to 300° C. with a compound R′R″NH in which R40 , R″ eachindependently denote hydrogen or a hydrocarbon residue with 1 to 20 Catoms.
 14. Process for producing a silicon boron carbide nitrideceramic, characterized in that an oligoborocarbosilazane orpolyborocarbosilazane as claimed in claim 12 or a silylalkylborane offormula (I) obtainable by a process as claimed in one of the claims 1 to5 or a silylalkylborazine as claimed in claim 9 is pyrolyzed in an inertor amrnmonia-containing atmosphere at temperatures between −200° C. and+2000° C. and subsequently calcined in an inert or ammonia-containingatmosphere at temperatures between 800° C. and 2000° C.
 15. Siliconboron carbide nitride ceramic obtainable by a process as claimed inclaim 14, characterized in that N—Si—C—B—N structural units are presentin the ceramic.
 16. Ceramic as claimed in claim 15, characterized inthat it is an amorphous ceramic.
 17. Ceramic as claimed in claim 15 or16, characterized in that it contains the elements N, Si, C and B in aquantity of more than 93% by weight.
 18. Process for the production of acomposite ceramic comprising at least one of the components SiC, Si₃N₄,BN, C and B₄C, characterized in that a silicon boron carbide nitrideceramic as claimed in one of the claims 15 to 17 is age-hardened attemperatures of more than 1400° C.
 19. Composite ceramic obtainable by aprocess as claimed in claim 15 by crystallizing a silicon boron nitrideceramic as claimed in one of the claims 15 to 17, characterized in thatSiC, Si₃N₄, BN, C or/and B₄C are molecularly dispersed therein. 20.Composite ceramic as claimed in claim 19, characterized in that it is anat least partially crystalline ceramic.
 21. Use ofoligoborocarbosilazanes or polyborocarbosilazanes as claimed in claim12, of silicon boron carbide nitride ceramics as claimed in claim 15 to17 or of composite ceramics as claimed in claim 19 or 20 to produceceramic powders, ceramic coatings, ceramic mouldings, ceramic foils,ceramic fibres or ceramic microstructures.
 22. Process for producing acompound of formula (I) (R)₃Si—C(R¹)(R²)—B(R)₂ in which R in each caseindependently represents a hydrocarbon with 1 to 20 C atoms, hydrogen,halogen, N(R′)(R″) or O(R′) where R′ and R″ independently of one anotherdenote hydrogen or a hydrocarbon with 1 to 20 C atoms and R¹ and R²independently denote hydrogen, halogen or a hydrocarbon with 1 to 20 Catoms characterized in that a silane of the general formula (VI)(R)₃Si—C(R¹)(R²)—X  in which X denotes hydrogen, halogen or silylresidues is reacted with a borane of the general formula (VII) B(R)₃  inthe presence of a suitable combination of catalyst, base and acid trapin which R in each case independently represents a hydrocarbon with 1 to20 C atoms, hydrogen, halogen, N(R′)(R″) or O(R′) where R′ and R″independently of one another represent hydrogen or a hydrocarbon with 1to 20 C atoms
 23. Process for producing a compound of formula (I)(R)₃Si—C(R′)(R²)—B(R)₂ in which R in each case independently representsa hydrocarbon with 1 to 20 C atoms, hydrogen, halogen, N(R′)(R″) orO(R′) where R′ and R″ independently of one another denote hydrogen or ahydrocarbon with 1 and 20 C atoms and R¹ and R² independently denotehydrogen, halogen or a hydrocarbon with 1 to 20 C atoms, characterizedin that a CH-acidic compound of the general formula (VIII)(R)₃Si—C(R¹)(R²)—H  is reacted in the presence of a suitable combinationof catalyst, base and acid trap with a borane of the general formula(IX) Y—B(R)₂  in which R is defined as above and Y represents halogen,NR′R″ or OR′ where R′ and R″ independently of one another denotehydrogen or a hydrocarbon with 1 to 20 C atoms.
 24. Process as claimedin claim 22 or 23, wherein an inorganic ion exchanger or a zeolite isused as the acid trap.